Screw-driver.



0. GROOS. sqanw nmvma. APPLICATION IIL'ED AUG. 5, 1912;

' Ptented Mar. 4, 1 913.

INVENTOR ATTORNEY STATES PATENT OFFICE.

'cnannns enoos, or San FRANCISCO, canronma.

SCREW-DRIVER.

Specification of Letters Patent. Application filed August 5, 1912. Serial No. 'nsflaoe.

Patented Mar. 4, 1913.

a torsional force applied to the screw driver,"

thus dispensing w1th the necessity of applying direct or longitudinal pressure thereto.-

It is a matter of common experience that,

in the majority'of cases, the greater part of the force exerted in screwing a screw in or out is expended in maintaining the screw.

driver in engagement with the screw. Unless pressure, and sometimes very great pressure, is applied to the screw driver, its operating end willslip out over the walls of the groove in the screw head, involving loss oftlme in re-applying the screw driver to the screw. Often the surface of the material worked upon isscratched and marred by the point or edge of the screw driver so slipping. After a screw driver has once slipped in this' rganner, it is more diflicult to prevent its recurrence, owing .to the fact that the edge of the groove has become rounded ofl, and offers lessresistance.

B torsibnal forceapplied thereto tends to hold it to the screw the moresecurely' the eater is the force applied, the necessity 0 direct inward pressure on the screw driverus eliminated, andthe force necwsary to be exerted is only that required to turn the screw in the material. I

In the accompanying drawing, Fi r 1 is a side view of a screw driver const cted in accordance with myinvention, Fig. 2 is an enlarged perspective .view of the operating end thereof; Figs. 3,. 4, 5 and 6 are views, similar to Fig. 2, of modified forms of the invention.

Referring to the drawing, 1 indicates one form-of my improved'screw'driver. Upon each side of the. operating terminal portion of said screw driver there are formed two rounded grooves 2,. commencin near the central longitudinal line. ofsai so constructing a screw driver that side, and increasing in depthand width to the respec-.v

3 of each groove terminates so close the end'of the' corresponding edge ofthe screw driver, that the portion 4 of the face of the screw driver engaging the wall of the groove in the screw is very small and forms a tooth, more or less pointed. Also the screw driver is made of material harder than the screw with which it is used. Consequently, on torsional pressure being applied in the proper direction to the. screw driver, the pressure is a plied to .the wall of the groove in the screw rom a surface of the screwdriver ofsuch small extent andsaid pressure is so concentrated that it produces a slight indentation therein, and'longitudinal movement of said tooth 4 along said wall is prevented. No inward or downward pressure is therefore required to maintain the screw driver in engagement with the screw, but only a rotational pressure. It will be observed that the strength of the screw driver is not materially diminished since at the center of its sides, where the greatesttorsional strain occurs, its thickness is not reduced. from that of the ordinary form. It will also be observed that to achieve the desired result, e thickness of.

the screw driver is not in reased, which would prevent it from being used with screws of the ordinary size.

In the modification shown in -Fig. 3, the

groove is shown as extendi'n in. pne direc tion only on each side from te mlddle portion of said side to the'edge thereof. In the modification shown. in Fi 4, the move 8 is, angular. In the modi cation s own in Fig.- 5, the groove 9 )is of uniform depth throu hout. This is also the case in the modi cation shown in Fig. 6, in which the groove 9 is angular. Y v

I ,am aware that, to obtain the result aimed at by my invention, it has been proposed to form the screw driver with a point or edge projecting beyondthe side of the'screw driver, butt tionable', because it necessitates the screw being formed with a wider groove, thus unplane of the :1

"s is objec- 99- duly weakeningthe-head of the screw or else reducing the thickness of the bit undul' weakening the screw driver if used wit screws now on* the'market.

I cla1m:--

1. A 'screw driver having formed in a sur- 1 face near its operating end, a groove extend? ing from one side of the middle of said surface to the adjacent edge of the screw driver, the middle portion of said surface,

at the same distance from the operating end, being flush with the top of the groove.

2. A screw driver having formed in a surface near its operating end a groove extending from one -side of the middle of said surface to the adjacent edge of the screw driver, and increasing gradually in depth,

10 the middle portion of said surface, at the osaoei 1 same distance from the operating end,-being flush with the top of the groove.

In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses.

CHARLES GROOS.

1 i v itnessesz FRANCIS M. VVRIGHT,

D. B. RICHARDS. 

